1. Field of the Invention and Related Art Statement
This invention relates to a filmy fluid (water) flow-forming pad (hereinafter referred to as a cooling pad) in a continuous casting apparatus for the direct production of cast sheets having a thickness of not more than 30 mm (e.g. sheet bar or the like) from molten metal, particularly molten steel (hereinafter referred to as a belt caster). More particularly, it relates to an improvement in the cooling pad which properly selects the size and arrangement of supply hole and discharge hole for cooling water so as to form a desired filmy water flow.
As a continuous casting apparatus for directly producing steel sheets such as sheet bar or the like from molten steel, there is a belt caster as disclosed in Japanese Patent laid open No. 57-100,851. In such a disclosed synchronous type belt caster, there are many systems, a typical example of which is shown in FIG. 1. This belt caster has usually such a structure that a casting space is defined by a pair of endlessly circulating metal belts 4, 5 oppositely arranged to each other at a given interval for retaining molten steel 2 over a predetermined distance, each of which being guided and supported through plural guide rolls 6a, 6b, 6c or 6'a, 6'b, 6'c and cooled by a filmy cooling water flow from the back face, and a pair of side plates disposed between the metal belts 4, 5 and positioned near the side edge portions of these metal belts.
Moreover, numeral 1 is a tundish, numeral 3 a pouring nozzle, numerals 7, 8 cooling pads arranged behind the metal belts 4, 5 for cooling these belts and forming a filmy water flow capable of supporting a static pressure of poured molten steel, numerals 9, 10 springs for tensioning the belts, and numeral 11 a cast sheet.
Since the static pressure of molten steel or semi-solidified cast sheet changes from molten steel level toward a cast sheet-drawing direction, the cooling pads 7, 8 act to balance the static pressure of molten steel at various stages of cast sheet (various positions in the cast sheet-drawing direction) by the pressure of the filmy cooling water flow. For this end, each cooling pad is provided at a side facing the respective metal belt with plural supply holes for the cooling water, each of which is provided at its top with a storing recess having a size enough to adjust the flow amount of the cooling water supplied.
In FIGS. 2 and 3 is shown a structure adopted in the conventional cooling pads 7 and 8, wherein each of plural oblong recesses 12 is disposed on the top portion of the corresponding water supply hole 15 for injecting the cooling water, which hole being formed in each of the cooling pads at its side facing the metal belt 4, 5, whereby a film flow of the cooling water is formed between the metal belt 4 or 5 and the cooling pad 7 or 8 to meet static pressure of molten steel and to uniformly cool the metal belt. Moreover, the oblong recesses 12 have usually a minor axis a of 50-150 mm and a major axis b of 100-200 mm and are so arranged that a transverse distance (l.sub.1) between centers of minor axes of mutual recesses is 200-400 mm and a longitudinal distance (l.sub.2 ) between centers of major axes of mutual recesses is 200-600 mm.
In the conventional cooling pad of such a structure, if it is intended to continuously cast thin slabs and sheet bars, the flow rate of the cooling water is considerably different between the water flowing portion 14 formed in the recess 12 and the filmy water portion 13 formed in an area other than the recess, so that there is caused the difference in the cooling strength, resulting in the wavy deformation of the metal belt. As a result, the liquid-tight contacting between the metal belt 4, 5 and the fixed side plate is injured to produce a gap therebetween, which causes the leakage of molten steel, casting troubles, and production of cast sheet having a poor shape such as fin and the like. And also, the surface of the cast sheet is not smoothened, which affects the surface properties of thin steel sheet after the rolling to cause the deterioration of the quality.